Boundary Lyer Theory

Fie. 2.511
Fig. 2 .5~
Fig. 2.5b
Fig. 2.5d
to thr1ns14vt:s. 'I'lrc only nrmngnncnt which shows ncnt.ral cqoilil,rium is t,hat with
- . 0.281 ([Cia. 2.8). vort,ex sl.rcet moves with n vcloc:it,y IL, which is slnallc\r
I,II:I.II t.Ilc flow vrIorii,y II in front of t,ho body. It cnn l)c rcpdetl as a highly idealized
pict,~~rr of t.hc mot,ion in the wake of (,hc body. The kinetic energy cont,ainetl in the
vrlocit,y ficltl of the vortcx strect must be continually created, as the body moves
t.llrongh tile fnitl. On the basis of this rcpresentrn.,tion it is possible t,o deduce an
exprrssion for t.hc drng from the perfect-fluid theory. Its ~nngnit,utle per nnit lengt,h
of tllr eYlindric:~l hotly is given hy
Fig. 2.7. KhrmQn vortex strcct, from
A. Tirn~nc [38]
Fig. 2.8. Strrnmlinm in nvortrx strrrt
(hll = 0 28). Thr fluid i8 nt rc~t, nt
infinity, and th~ vortrx street move8
Circdur cylittder. 'l'hc frequency wit,lr which vor1,irc~s arr shrtl in a I